Analysis of bacteriophage Mu and λ-Mu hybrid DNAs by specific endonucleases

Abstract

The DNAs of plaque-forming particles bearing various portions of bacteriophages λ and Mu were cleaved by the specific endonucleases of Hemophilus influenzae and analyzed by polyacrylamide gel electrophoresis. Our extensive mapping data on λ and Mu DNA allowed us to identify the parts of each parent in the hybrids. The technique revealed that both ends of Mu DNA are heterogeneous in size, and suggested that a portion of DNA at the immunity end of vegetative Mu is not inserted in the prophage. The known ability of Mu to invert a specific part of its own DNA (G loop inversion) was observed mainly in phage grown by induction of a lysogen, and the gene involved was deduced to lie within, or at least very close to, the G loop region itself. The mode of growth of Mu, by lytic infection or by induction of a lysogen, also affected the phage DNA in its pattern of modification. Thus a specific endonuclease, Hin II, failed to cleave the DNA of Mu induced from a lysogen, even though it cleaved at several sites the DNA of phage grown by lytic infection.